Bad stumble at startup. Injector?

So I've had a rough idle for a while. I have 6 new plugs installed by dealer at last service, coils 1,2 and 6 are new due to failures, and 3 injectors were replaced under recall with the HPFP. I chalked the rough idle up to needing a valve cleaning. This morning when i started the car it ran really rough for a couple of seconds and was obviously missing. No codes though of course. This sounds like a leaky injector to me. Any thoughts from the eperts? Since there are no codes what's the easiest way to find which injector it is if it is an injector? Since the plugs are brand new (less than 1k mi) I assume one plug will look different than the others. Black i assume?

I don't think its the e85. I'm running a backend flash and afr/fuel pressure are fine. I have a new fuel pressure sensor along with the other parts I mentioned. It stumbles at idle when the car is warm too just not as bad. I'm pretty certain it's an injector. Ill be pulling all the plugs Monday to check them out. I've ordered 3 coils too just as a preventive maintenance deal to replace the 3 I haven't replaced yet.

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I'm not getting long cranks at all. Just a VERY rough idle. When the car first starts you can def hear the stumbles and feel the car shake. It does this when the car is warm too, at idle, just not nearly as bad.

Well let the car sit last night. Pulled the plugs one at a time this morning before starting it. Started at 1. All was good till I got to 6. 6 had fuel all over it and was super black. Guess I found the problem. Of course it's the hardest one to get to. Oh we'll. it's sad though that 3 trips to the dealer and they "didn't feel the rough idle".

I've had the "pleasure" of diagnosing misfires and cold-start roughness on a few N54s lately, and I think there may be more to this PCV/valve cover issue. If you still have roughness on more gasoline than ethanol, change more parts, and still have stumbling or roughness, let us know here. I have an hypothesis that not only is the PCV system allowing too much oil into the intake, but it also runs RIGHT into cylinder 5. No catch can will cure this, because I'm referring to the channel that allows the intake ports to pull crankcase gasses straight from the PCV valve in the valve cover.

I've had the "pleasure" of diagnosing misfires and cold-start roughness on a few N54s lately, and I think there may be more to this PCV/valve cover issue. If you still have roughness on more gasoline than ethanol, change more parts, and still have stumbling or roughness, let us know here. I have an hypothesis that not only is the PCV system allowing too much oil into the intake, but it also runs RIGHT into cylinder 5. No catch can will cure this, because I'm referring to the channel that allows the intake ports to pull crankcase gasses straight from the PCV valve in the valve cover.

Hm I guess that explains whenever I do valve cleanings, #5 valves always look like just a block of carbon going up and down.

Yep. I did mine last Fall when I bought the car. 3 of 6 ports were wet with oil, the rest just dry carbon. Horrible, thick, gunky buildup, but they cleaned up nicely.

Fast forward 16k miles and a year later, I decided to recheck. Water/meth was probably no help. But I also noticed that now all 6 ports were wet with oil. The IC and intake manifold were not swimming with oil, so the oil must be coming from the channel on the VC. Additionally, the area in port #5 was almost clean around the PCV port. This indicates a lot of oil coming in. The valve stems on #5 had tar/carbon balls on them, too, while the others were just dirty. I cleaned all the ports again (the BMW walnut blasting tool is FAN-friggin-TASTIC), and buttoned up.

So the next weekend (about 17 days ago) I delved into the valve cover/PCV/gasket issue. I wanted to make sure I took care of any possible issues to prevent excess oil from fouling up my clean intake ports, for a while, at least. I remove the VC and inspected. Rob Beck's info on the PCV was very helpful and informative. I noticed no leaks around any of the port passages into the valve cover PCV channel, and no other oil leaks around the VC gasket at all. I removed the PCV valve from the cover and checked - closes against manifold pressure, no sludge, no nothing. Cleaned it anyway just for good measure. RB PCV valve upgrade soon to follow...

But I also, while it was all apart, cleaned the everloving sh--stuff out of the inside of the valve cover. Brake cleaner, then purple degreaser and a pressure washer. I also did the same for the vent tube from the cover to the rear turbo inlet pipe. That tube has a simple one-way flapper to prevent the recirc/DV from pushing air into the engine, but it also has a bypass port about 4mm in diameter. Push air from the turbo inlet toward the motor, and the valve shuts but still allows flow through the port. Push air from the engine to the turbo inlet pipe, and it's wide open.

So I cleaned the hell out of it, too, and reinstalled. Reinstalled the valve cover (dried thoroughly with compressed air and a fan) using Hylomar on the head and rubber gasket around the PCV to intake passages.

I will then pull the intake again and recheck how bad or good the intake ports look and for presence of liquid oil. I was just intrigued by the fact that only half my ports had liquid oil in them the first time I cleaned it last year, so I am hoping that PCV system maintenance will quell this issue. Other N54s we've cleaned here at the shop have had varying amounts of liquid oil in the intake.

The biggest thing I noted was that the PCV valve and its channel that runs along the side of the valve cover seem to allow much more oil to run straight down into #5.

I'm also running Motul 5W40 X-cess. I have zero oil consumption between changes, and the motor was literally brand-new clean inside when I had the valve cover off. 61k miles so far...

Yep. I did mine last Fall when I bought the car. 3 of 6 ports were wet with oil, the rest just dry carbon. Horrible, thick, gunky buildup, but they cleaned up nicely.

Fast forward 16k miles and a year later, I decided to recheck. Water/meth was probably no help. But I also noticed that now all 6 ports were wet with oil. The IC and intake manifold were not swimming with oil, so the oil must be coming from the channel on the VC. Additionally, the area in port #5 was almost clean around the PCV port. This indicates a lot of oil coming in. The valve stems on #5 had tar/carbon balls on them, too, while the others were just dirty. I cleaned all the ports again (the BMW walnut blasting tool is FAN-friggin-TASTIC), and buttoned up.

So the next weekend (about 17 days ago) I delved into the valve cover/PCV/gasket issue. I wanted to make sure I took care of any possible issues to prevent excess oil from fouling up my clean intake ports, for a while, at least. I remove the VC and inspected. Rob Beck's info on the PCV was very helpful and informative. I noticed no leaks around any of the port passages into the valve cover PCV channel, and no other oil leaks around the VC gasket at all. I removed the PCV valve from the cover and checked - closes against manifold pressure, no sludge, no nothing. Cleaned it anyway just for good measure. RB PCV valve upgrade soon to follow...

But I also, while it was all apart, cleaned the everloving sh--stuff out of the inside of the valve cover. Brake cleaner, then purple degreaser and a pressure washer. I also did the same for the vent tube from the cover to the rear turbo inlet pipe. That tube has a simple one-way flapper to prevent the recirc/DV from pushing air into the engine, but it also has a bypass port about 4mm in diameter. Push air from the turbo inlet toward the motor, and the valve shuts but still allows flow through the port. Push air from the engine to the turbo inlet pipe, and it's wide open.

So I cleaned the hell out of it, too, and reinstalled. Reinstalled the valve cover (dried thoroughly with compressed air and a fan) using Hylomar on the head and rubber gasket around the PCV to intake passages.

I will then pull the intake again and recheck how bad or good the intake ports look and for presence of liquid oil. I was just intrigued by the fact that only half my ports had liquid oil in them the first time I cleaned it last year, so I am hoping that PCV system maintenance will quell this issue. Other N54s we've cleaned here at the shop have had varying amounts of liquid oil in the intake.

The biggest thing I noted was that the PCV valve and its channel that runs along the side of the valve cover seem to allow much more oil to run straight down into #5.

I'm also running Motul 5W40 X-cess. I have zero oil consumption between changes, and the motor was literally brand-new clean inside when I had the valve cover off. 61k miles so far...

I had been changing my girls oil in her 335 every 5-6k, zero consumption as well. Same goes for my car as well when I had it. I assume there is no way to keep the motor from pulling crankcase gasses via the head ports, unless there is a way to block it off?

Ive also noticed that the cars that are run harder and do less putting around/idling, have way less buildup. I did a cleaning on a 135 roadrace car, 30k on it and all the ports just had a light coat of dried up carbon on them..same when for a street car that had the ever loving crap beat out of it. I figure under boost the PCV system closes off, and keeps most of that stuff out.

James have you tried out RBs upgraded Pcv? I have one and a catch can but those just went on over the last 10k mi. I'm sure I need an intake valve cleaning. I wonder though if the upgraded Pcv will help.

I cleaned the valves the same time I installed the upgraded PCV, about 4000km ago. I figured I'd borescope in Dec and do another cleaning next summer. Much like James, I had wet oil from every PCV port into the intake valvetrain as well.